Ni原子双飞秒脉冲激光诱导击穿光谱的信号增强研究

在大气环境下采用波长为800nm,脉宽为30fs的飞秒激光研究了Ni的双脉冲激光诱导击穿光谱,与单飞秒脉冲激光诱导击穿光谱相比,双飞秒脉冲在最优的双脉冲相对延时下,其信号强度增强接近10倍,实验研究了双脉冲相对延时在0-1300ps范围内不同延时对激光诱导击穿光谱信号强度增强因子的影响。整个相对延时区域可以分为三个阶段：在0-50ps区域内信号增强因子是一个持续增大的过程,在50ps左右,达到一个最大值;在50-300ps区域内,信号增强因子呈现出一个先下降后上升的过程;在300-1300ps,信号增强因子基本保持不变。     

近红外光谱法预测粗皮桉木材气干密度的影响因素分析

采用近红外光谱分析技术,对粗皮桉木材气干密度校正模型的影响因素进行比较研究.使用直接测量法测量了粗皮桉木材的气干密度,并用近红外光谱仪采集试样的近红外漫反射光谱,对不同切面、厚度、含水率和粗糙度的粗皮桉木材试样的原始光谱进行二阶导数预处理并选择一定光谱段建立回归模型.以50～140个试样作为校正集建立木材气干密度的偏最...     

双曲余弦高斯列阵光束在湍流大气中的光束传输因子

本文推导出了双曲余弦高斯(ChG)列阵光束在湍流大气中的光束传输因子( M ^{2因子)的解析公式,并采用相对 M 2因子研究了湍流对 M 2因子的影响.研究表明,在湍流大气中 M 2因子不再是一个传输不变量,湍流使得 M 2因子增大.非相干合成情况下, M 2因子随着传输距离、光束参数、相对子光束间距和子光束数目的增大而增大.相干合成情况下, M 2因子随光束参数和相对子光束间距的增大呈现振荡上升.相干合成情况下的 M 2因子比 关键词： M2因子)')" href="#">光束传输因子(M2因子) 光束质量 双曲余弦高斯列阵光束 大气湍流}     

基于M2因子测量的大气湍流参数的确定方法

基于广义惠更斯-菲涅尔原理以及大气湍流理论,推导出部分相干光束在大气湍流中传输的光束传输M ^{2因子的解析表达式.定量分析了表征大气湍流参数的折射率结构常数 C2_n}和涡旋内尺度 l _{0对 M ^{2因子的影响,并由此提出了一种通过实验测量大气湍流中光束的 M 2因子,进而确定出大气湍流参数的新方法.研究结果表明,由于大气湍流对相干性好的光束影响更为明显,在测量中可采用具有高相干性的基模高斯光束作为测量光源,而测量装 关键词： 2因子')" href="#">光束传输 M 2因子 大气湍流参数 湍流折射率结构常数 湍流涡旋内尺度}}     

高功率光纤激光器二级抽运技术的理论分析

从理论上分析了高功率光纤激光器直接抽运和二级抽运的斜率效率和热管理问题. 计算结果表明:波长为975 nm的激光直接抽运产生波长为1070 nm的激光时,理论斜率效率为80%,但当抽运光功率为10 kW时,在强制水冷条件下纤芯极值温度也难以降到150 ℃以下;在二级抽运技术中,波长为1018 nm的激光抽运产生波长为1070 nm的激光时,若采用传统的包层抽运技术,其斜率效率不足20%,如果抽运功率填充因子由0.0025提高到0.1,则理论上斜率效率可由18.5%提高到80.9%,从而总斜率效率由15.5 关键词： 二级抽运 功率填充因子 斜率效率 热管理     

Study of heterogeneous interaction in binary mixtures of 2-methoxyethanol-water using dielectric relaxation spectroscopy

The dielectric relaxation measurements on binary mixtures of 2-methoxyethanol with water have been carried out over entire concentrations and at temperature range of 0 °C to 25 °C using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectra of 2-methoxyethanol/water mixtures were fitted using Havriliak-Negami equation. The static dielectric constant and relaxation time for all concentrations were obtained using least square fit method. The principal relaxation time is small if compared to that of corresponding alcohol/water mixtures this may be due to the hydrogen bonding ether oxygen in the 2-ME-water system. Excess dielectric properties, Kirkwood correlation factor, thermodynamic properties and Bruggeman factor are also determined and the results are interpreted in terms of heterogeneous interactions among the unlike molecules due to hydrogen bonding.     

耦合微盘及带输出波导的单微盘腔的耦合模式特性

光学微腔具有很高的品质因子和很小的模式体积,在光电子器件研究方面具有重要的应用价值.运用时域有限差分(FDTD)法和Padé近似频谱分析法模拟研究了耦合微盘及带输出波导的单微盘微腔由于空间对称性破坏导致的模式耦合现象;特别计算了耦合模式的场分布和品质因子,并由场分布得出不同角量子数模式的能量比例.对耦合微盘,模式耦合引...     

Structure factor of ferrofluids with chain aggregates: Theory and computer simulations

In this paper we present theoretical and simulation results on the structure factor of mono- and bidisperse ferrofluids with chain aggregates, both with and without an applied external magnetic field. Chain distribution is obtained by the density functional theory (DFT). The radial distribution function (RDF) is calculated directly on the basis of the chain distribution and Fourier transformed to calculate the structure factor. An extensive comparison of the theoretical predictions to the results of the molecular dynamics computer simulations is provided. The proposed combined approach allows to elucidate the connection between experimentally observed small angle neutron scattering (SANS) images and the ferrofluid microstructure.     

Heavy quarks at RHIC and LHC within a partonic transport model

Production and space-time evolution of heavy quarks in central and non-central heavy-ion collisions at RHIC and LHC are studied with the partonic transport model Boltzmann Approach of MultiParton Scatterings (BAMPS). In addition to the initially created heavy quarks in hard parton scatterings during nucleon-nucleon collisions, secondary heavy quark production in the quark-gluon plasma is investigated and the sensitivity on various parameters is estimated. In BAMPS heavy quarks scatter with particles of the medium via elastic collisions, whose cross section is calculated with the running coupling and a more precise implementation of Debye screening. In this framework, we compute the elliptic flow and nuclear modification factor of heavy quarks and compare it to the experimental data.     

RL与C并联谐振电路品质因数精确值的计算

在谐振电路中,品质因数是一个重要的参数.一般教材对RLC串联谐振电路和RLC并联谐振电路的品质因数讨论较多,品质因数一般定义为电压或电流之间的比值.对实际应用中较为常见的电感线圈和电容并联谐振电路,即RL与C并联谐振电路的品质因数的讨论较少.本文根据谐振电路储能与耗能所定义的品质因数,计算了实际中常用的电感线圈和电容并...